Electronic systems using optical waveguide interconnects formed throught a semiconductor wafer

ABSTRACT

An integrated circuit with a number of optical waveguides that are formed in high aspect ratio holes. The high aspect ratio holes extend through a semiconductor wafer. The optical waveguides include a highly reflective material that is deposited so as to line an inner surface of the high aspect ratio holes which may be filled with air or a material with an index of refraction that is greater than 1. These metal confined waveguides are used to transmit signals between functional circuits on the semiconductor wafer and functional circuits on the back of the wafer or beneath the wafer.

This application is a continuation of U.S. application Ser. No.10/435,172 filed on May 8, 2003, now U.S. Pat. No. 6,995,441, which isdivisional of U.S. application Ser. No. 09/618,648 filed on Jul. 18,2000, now U.S. Pat. No. 6,777,715, which is a divisional of U.S.application Ser. No. 09/031,961 filed on Feb. 26, 1998, now U.S. Pat.No. 6,090,636, all of which are incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to the field of integratedcircuits and, in particular, to integrated circuits using opticalWaveguide interconnects formed through a semiconductor wafer and methodsfor forming same.

BACKGROUND OF THE INVENTION

Electrical systems typically use a number of integrated circuits thatare mounted on a printed circuit board. The individual integratedcircuits of the system are typically fabricated on different wafers.Each wafer is tested and separated into individual dies or chips.Individual chips are then packaged as individual integrated circuits.Each integrated circuit includes a number of leads that extend from thepackaging of the circuit. The leads of the various integrated circuits,are interconnected to allow information and control signals to be passedbetween the integrated circuits such that the system performs a desiredfunction. For example, a personal computer includes a wide variety ofintegrated circuits, e.g., a microprocessor and memory chips, that areinterconnected on one or more printed circuit boards in the computer.

While printed circuit boards are useful for bringing together separatelyfabricated and assembled integrated circuits, the use of printed circuitboards creates some problems which are not so easily overcome. Forexample, printed circuit boards consume a large amount of physical spacecompared to the circuitry of the integrated circuits which are mountedto them. It is desirable to reduce the amount of physical space requiredby such printed circuit boards. Further, assuring the electricalintegrity of interconnections between integrated circuits mounted on aprinted circuit board is a challenge. Moreover, in certain applications,it is desirable to reduce the physical length of electricalinterconnections between devices because of concerns with signal loss ordissipation and interference with and by other integrated circuitrydevices.

A continuing challenge in the semiconductor industry is to find new,innovative, and efficient ways of forming electrical connections withand between circuit devices which are fabricated on the same and ondifferent wafers or dies. Relatedly, continuing challenges are posed tofind and/or improve upon the packaging techniques utilized to packageintegrated circuitry devices. As device dimensions continue to shrink,these challenges become even more important.

For reasons stated above, and for other reasons stated below which willbecome apparent to those skilled in the art upon reading andunderstanding the present specification, there is a need in the art foran improved technique for interconnecting individual integrated circuitsin an electronic system.

SUMMARY OF THE INVENTION

The above mentioned problems with integrated circuits and other problemsare addressed by the present invention and will be understood by readingand studying the following specification. Integrated circuits aredescribed which use optical waveguides that extend through the thicknessof a semiconductor substrate or wafer so as to allow communicationbetween integrated circuits formed on opposite sides of a single wafer,on opposite sides of two wafers that are bonded together, formed onwafers in a stack that are bonded together, or other appropriateconfiguration of wafers.

In particular, in one embodiment, a method for interconnecting first andsecond integrated circuits is provided. The first integrated circuit isformed on a working surface of a first semiconductor substrate. At leastone high aspect ratio hole is formed through the first semiconductorsubstrate. The high aspect ratio hole is lined with a material having ahigh reflectivity for light to form an optical waveguide. The firstintegrated circuit is coupled to the second integrated circuit throughthe optical waveguide. In one embodiment, the second integrated circuitis formed on a second surface of the first semiconductor substrate,opposite the working surface of the first semiconductor substrate. Inanother embodiment, the second integrated circuit is formed on a workingsurface of a second semiconductor substrate. The second semiconductorsubstrate is bonded to the first semiconductor substrate such that thefirst and second integrated circuits are coupled together through theoptical waveguide in the first semiconductor substrate. In anotherembodiment, the surfaces of the first and second semiconductorsubstrates that are bonded together are located on sides of the firstand second semiconductor substrates that are opposite the workingsurfaces of the first and second semiconductor substrates, respectively.

In another embodiment, an electronic system is provided. The electronicsystem includes at least one semiconductor wafer. The electronic systemincludes a number of integrated circuits. At least one integratedcircuit is formed on the at least one semiconductor wafer. The at leastone semiconductor wafer includes at least one optical waveguide formedin a high aspect ratio hole that extends through the thickness of the atleast one semiconductor wafer. Further, at least one optical transmitterand at least one optical receiver are associated with the at least oneoptical waveguide. The optical transmitter and optical receiver transmitoptical signals between selected integrated circuits of the electronicsystem.

In another embodiment, an integrated circuit is provided. The integratedcircuit includes a functional circuit formed on a wafer. A number ofoptical waveguides are formed in high aspect ratio holes that extendthrough the wafer. The optical waveguides include a highly reflectivematerial that is deposited so as to line an inner surface of the highaspect ratio holes.

In another embodiment, a method for forming an integrated circuit in asemiconductor wafer with an optical waveguide that extends through thesemiconductor wafer is provided. A functional circuit is formed in afirst surface of a semiconductor wafer. A number of etch pits are formedin the first surface of the semiconductor wafer at selected locations inthe functional circuit. An anodic etch of the semiconductor wafer isperformed such that high aspect ratio holes are formed through thesemiconductor wafer from the first surface to a second, oppositesurface. A highly reflective layer of material is formed on an innersurface of the high aspect ratio holes such that the holes have anopening extending through the semiconductor wafer with a diameter thatis at least three times the cut-off diameter. The optical fiber isselectively coupled to the functional circuit.

In another embodiment, a method for forming an optical waveguide througha semiconductor substrate is provided. The method includes forming atleast one high aspect ratio hole through the semiconductor substratethat passes through the semiconductor substrate from a first workingsurface to a surface opposite the first working surface. Further, thehigh aspect ratio hole is lined with a material having a highreflectivity for light. In one embodiment, the at least one high aspectratio hole is etched in the semiconductor substrate using an anodicetch. In one embodiment, etch pits are formed in the working surface ofthe semiconductor substrate prior to the anodic etch such that the atleast one high aspect ratio hole is formed at the location of the etchpits. In one embodiment, the high aspect ratio holes are lined with alayer of tungsten and a layer of aluminum. In one embodiment, thetungsten layer is formed using a silicon reduction process and a silanereduction process. In one embodiment, the high aspect ratio hole islined with a layer of aluminum material. In one embodiment, the layer ofaluminum material has a thickness of approximately 300 angstroms. In oneembodiment, the optical waveguide includes an opening extending throughthe semiconductor substrate with a cross-sectional diameter of at leastthree times the cut-off diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C are elevational views of exemplary embodiments ofintegrated circuits that use a semiconductor wafer having an opticalwaveguide formed in an high aspect ratio hole that extends through thesemiconductor wafer according to the teachings of the present invention.

FIGS. 2, 3, 4, 5, and 6 are views of a semiconductor wafer at variouspoints of an illustrative embodiment of a method for forming an opticalwaveguide through the wafer according to the teachings of the presentinvention.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific illustrative embodiments in which theinvention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention, and it is to be understood that other embodiments may beutilized and that logical, mechanical and electrical changes may be madewithout departing from the spirit and scope of the present invention.The following detailed description is, therefore, not to be taken in alimiting sense.

In the following description, the terms wafer and substrate areinterchangeably used to refer generally to any structure on whichintegrated circuits are formed, and also to such structures duringvarious stages of integrated circuit fabrication. Both terms includedoped and undoped semiconductors, epitaxial layers of a semiconductor ona supporting semiconductor or insulating material, combinations of suchlayers, as well as other such structures that are known in the art.

The term “horizontal” as used in this application is defined as a planeparallel to the conventional plane or surface of a wafer or substrate,regardless of the orientation of the wafer or substrate. The term“vertical” refers to a direction perpendicular to the horizonal asdefined above. Prepositions, such as “on”, “side” (as in “sidewall”),“higher”, “lower”, “over” and “under” are defined with respect to theconventional plane or surface being on the top surface of the wafer orsubstrate, regardless of the orientation of the wafer or substrate.

FIG. 1A is an elevational view of an embodiment of the presentinvention. Electronic system 105 a includes semiconductor wafer 100 a.Semiconductor wafer 100 a includes at least one optical waveguide 102 athat provides a path for transmitting signals between functional circuit108 a on a first working surface of semiconductor wafer 100 a andfunctional circuit 109 a on a second, opposite working surface ofsemiconductor wafer 100 a. It is noted that a number of opticalwaveguides can be formed through semiconductor wafer 100 a. The singleoptical waveguide 102 a is shown by way of example and not by way oflimitation.

Optical waveguide 102 a is formed in a high aspect ratio hole insemiconductor wafer 100 a. The high aspect ratio hole is formed using,for example, an anodic etching technique as described in more detailbelow. Typically, the high aspect ratio holes have an aspect ratio inthe range of approximately 100 to 200. Conventionally, a semiconductorwafer has a thickness in the range of approximately 100 to 1000 microns.Thus, the high aspect ratio holes used to form the optical waveguidescan be fabricated with a diameter that is in the range fromapproximately 0.5 microns to approximately 10 microns.

Optical waveguide 102 a is coupled to functional circuits 108 a and 109a. For example, optical transmitter 104 a is coupled to one end ofoptical waveguide 102 a and optical receiver 106 a is coupled to asecond, opposite end of optical waveguide 102 a. Optical transmitter 104a is also coupled to a node of functional circuit 108 a and opticalreceiver 106 a is coupled to a node of functional circuit 109 a. In oneembodiment, optical transmitter 104 a comprises a gallium arsenidetransmitter that is bonded to a surface of semiconductor wafer 100 ausing conventional wafer bonding techniques. In this embodiment, opticalreceiver 106 a comprises a silicon photodiode detector formed in asurface of semiconductor wafer 100 a. In other embodiments, otherappropriate optical receivers and transmitters may be used to transmitsignals over optical waveguide 102 a.

Optical waveguides 102 a include reflective layer 110 a and hollow core112 a. Reflective layer 110 a comprises a highly reflective materialsuch as aluminum or other material that can be used to line the highaspect ratio hole with a mirror-like surface. When aluminum is used, athickness of approximately 300 angstroms effectively achieves fullreflectivity.

Reflective layer 110 a serves to contain optical waves within opticalwaveguide 102 a. This is desirable for at least two reasons. First, thisreduces loss of the optical signal into the surrounding semiconductormaterial of wafer 100 a. Second, this also reduces photogeneration ofcarriers in the surrounding semiconductor material of wafer 100 a thatmight interfere with normal operation of other integrated circuitry inelectrical system 105 a.

Optical waveguide 102 a should have sufficient diameter to be abovecut-off for transmission of light waves. Equation (1) can be used todetermine the cut-off diameter, D₀, for transmission of optical waves inthe optical waveguide. Optical waveguide 102 a should have a diameterthat is at least three times the cut-off diameter. In some cases, adiameter that is ten times the cut-off diameter can be used.

$\begin{matrix}{D_{0} = {0.59\frac{\lambda_{0}}{n}}} & (1)\end{matrix}$The term λ₀ is the free-space wavelength and n is the index ofrefraction for the material within the optical guide. For a case whereλ₀ is 1 micron and n is 1 (e.g., air in the center of the waveguide), a6 micron diameter for optical waveguide 102 is reasonable.

It is noted that optical waveguide 102 a could be filled with a materialwith an index of refraction that is greater than 1. However, thematerial used for reflective layer 110, e.g., aluminum, would have tosurvive the deposition of the material.

Optical waveguides can be added to circuits using a conventional layoutfor the circuit without adversely affecting the surface arearequirements of the circuit. Conventional circuits typically includepads formed on the top surface of the semiconductor wafer that are usedto connect to leads of the integrated circuit through bonding wires.Advantageously, the bonding wires of conventional circuits can bereplaced by optical waveguides 102 a to allow signals to be passedbetween various integrated circuits of electrical system 105 a withoutthe need to attach the individual integrated circuits to a printedcircuit board. This allows a substantial space savings in the design ofelectrical systems along with overcoming concerns related to signal lossor dissipation and interference with and by other integrated circuitrydevices in the electrical system.

FIGS. 1B and 1C show additional embodiments of electronic systems usingoptical waveguides formed through integrated circuits to interconnectvarious integrated circuits. In the embodiment of FIG. 1B, integratedcircuits 108 b and 109 b are formed in working surfaces of semiconductorwafers 100 b and 101 b. Surfaces opposite the working surfaces ofsemiconductor wafers 100 b and 101 b are bonded together usingconventional wafer bonding techniques. Optical waveguide 102 b transmitssignals between integrated circuits 108 b and 109 b. A portion ofoptical waveguide 102 b is formed in each of the semiconductor wafers100 b and 101 b. In the embodiment of FIG. 1C, semiconductor wafers 100c and 101 c are stacked with the working surface of semiconductor wafer101 c beneath the surface of semiconductor wafer 100 c that is oppositethe working surface of semiconductor wafer 100 c. In this embodiment,optical waveguide 102 c is formed within semiconductor wafer 100 c.

FIGS. 2, 3, 4, 5, and 6 are views of semiconductor wafer 200 at variouspoints of an illustrative embodiment of a method for forming opticalwaveguides through a semiconductor wafer according to the teachings ofthe present invention. Functional circuit 202 is formed in an activeregion of semiconductor wafer 200. For purposes of clarity, the Figuresonly show the formation of two optical waveguides through semiconductorwafer 200. However, it is understood that with a particular functionalcircuit any appropriate number of optical waveguides can be formed.Essentially, the optical waveguides are formed in the same space on thesurface of semiconductor wafer 200 that is conventionally used to formbonding pads for leads. In a conventional circuit, the leads of theintegrated circuit are connected to a printed circuit board which routessignals to other integrated circuits. The optical waveguidesadvantageously remove the need for a printed circuit board tointerconnect the functional circuits formed on individual semiconductorwafers.

As shown in FIG. 2, photo resist layer 204 is formed on surface 206 ofsemiconductor substrate 200. Photo resist layer 204 is patterned toprovide openings 208 at points on surface 206 where high aspect ratioholes are to be formed through semiconductor wafer 200.

As shown in FIG. 3, etch pits 210 are formed by standard alkalineetching through openings 208 in photo resist layer 204. Photo resistlayer 204 is then removed.

FIG. 4 is a schematic diagram that illustrates an embodiment of a layoutof equipment used to carry out an anodic etch that is used to form highaspect ratio holes 250 of FIG. 5. Typically, holes 250 have an aspectratio in the range of 100 to 200. Bottom surface 262 of semiconductorwafer 200 is coupled to voltage source 234 by positive electrode 230.Further, negative electrode 232 is coupled to voltage source 234 and isplaced in a bath of 6% aqueous solution of hydrofluoric acid (HF) onsurface 206 of semiconductor wafer 200.

In this example, illumination equipment 236 is also included becausesemiconductor wafer 200 is n-type semiconductor material. When p-typesemiconductor material is used, the illumination equipment is notrequired. Illumination equipment 236 assures that there is a sufficientconcentration of holes in semiconductor wafer 200 as required by theanodic etching process. Illumination equipment 236 includes lamp 238, IRfilter 240, and lens 242. Illumination equipment 236 focuses light onsurface 262 of semiconductor wafer 200.

In operation, the anodic etch etches high aspect ratio holes throughsemiconductor wafer 200 at the location of etch pits 210. Voltage source234 is turned on and provides a voltage across positive and negativeelectrodes 230 and 232. Etching current flows from surface 206 topositive electrode 230. This current forms the high aspect ratio holesthrough semiconductor wafer 200. Further, illumination equipmentilluminates surface 262 of semiconductor wafer 200 so as to assure asufficient concentration of holes for the anodic etching process. Thesize and shape of the high aspect ratio holes through semiconductorwafer 200 depends on, for example, the anodization parameters such as HFconcentration, current density, and light illumination. An anodicetching process is described in V. Lehmann, The Physics of MacroporeFormation in Low Doped n-Type Silicon, J. Electrochem. Soc., Vol. 140,No. 10, pp. 2836–2843, October 1993, which is incorporated herein byreference.

As shown in FIGS. 5 and 6, reflective layer 254 is formed on innersurface 252 of high aspect ratio holes 250. In one embodiment,reflective layer 254 comprises a metallic mirror that is deposited witha self-limiting deposition process. This produces a reflective surfacefor optical waveguide 256 that is substantially uniform. Waveguide 256also has a center void 258 that is essentially filled with air.

A two-step, selective process is used, for example, to deposit tungstenas a portion of reflective layer 254. This is a low-pressure chemicalvapor deposition (LPCVD) process. In this process, atoms insemiconductor wafer 200, e.g., silicon, are replaced by tungsten atomsin a reaction gas of WF₆. This is referred to as a “silicon reductionprocess.” The limiting thickness of this process is approximately 5 to10 nanometers. This thickness may not be sufficient for reflective layer254. Thus, a second reduction process can be used to complete thedeposition of tungsten. This second reduction step uses silane orpolysilane and is thus referred to as a “silane reduction.” The silanereduction process also uses WF₆. In this process, the deposition rate ishighly dependent on the temperature and the reaction gas flow rate. Forexample, at 300° Celsius, tungsten deposits at a rate as high as 1micron per minute using WF₆ flow rate of 4 standard cubic centimetersper minute in a cold-wall chemical vapor deposition (CVD) reactor.

When tungsten is used for reflective layer 254, a thin film of amaterial with a higher reflectivity is deposited on the tungstenmaterial. For example, an aluminum film can be deposited at lowtemperature, e.g., in the range from 180° to 250° Celsius.Dimethylaluminum hydride is often used as the precursor when depositingaluminum because of its thermal stability and high vapor pressure.Further, the deposition of aluminum can be carried out with hydrogen asa carrier gas with wafer 200 maintained at a temperature ofapproximately 250° Celsius and a pressure of approximately 5 Torr. Thetypical deposition rate for this process is less than 100 nanometers perminute. It is noted that the aluminum could be deposited on a silicideas well. Aluminum can be deposited on a silicide at a much lowertemperature, e.g., 100° Celsius, with a very high deposition rate usingdimethylethylaminealane (DMEAA). Deposition rates of 500 nanometers perminute have been reported using this technique at 150° Celsius with nocarrier gas, and approximately 70 nanometers per minute at 100° Celsius.

CONCLUSION

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiment shown. This application isintended to cover any adaptations or variations of the presentinvention. For example, the diameter of the opening in the opticalwaveguides can be adjusted as needed for a specific application.Further, process parameters can be varied so as to create high aspectratio holes with sufficient diameter and reflective layers of sufficientthickness for a particular application. Other appropriate materials andprocesses can be used to form the reflective layer of the opticalwaveguides. Further, it is noted that the waveguides can be used totransmit signals in either direction through a semiconductor wafer.Further, electronic systems can include more than two semiconductorwafers with sufficient optical waveguides formed through thesemiconductor wafers to allow signals to be communicated between theintegrated circuits of the various semiconductor wafers.

Advantageously, using optical waveguides according to the teachings ofthe present invention allows electronic systems to be constructed inless physical space compared to conventional electronic systems byremoving the need for large printed circuit boards to interconnectvarious integrated circuits. This also provides the advantage ofreducing the cost of packaging integrated circuits for a particularelectronic system by allowing a number of circuits to be packagedtogether. Further, using the optical waveguides assures the electricalintegrity of interconnections between integrated circuits by reducingthe physical length of electrical interconnections between devices. Thisreduces concerns with signal loss or dissipation and interference withand by other integrated circuitry devices.

1. An electronic system, comprising: a semiconductor substrate with ahole that includes an aspect ratio of at least approximately 100; anintegrated circuit formed with the semiconductor substrate; an opticalwaveguide formed in the hole in the semiconductor substrate; and anoptical transmitter and an optical receiver associated with the opticalwaveguide that transmits optical signals between selected integratedcircuits of the electronic system.
 2. The electronic system of claim 1,wherein the hole has a diameter in the range of approximately 0.5microns to approximately 10 microns.
 3. The electronic system of claim1, wherein the optical waveguide includes a metallic mirror lining inthe hole.
 4. The electronic system of claim 3, wherein the metallicmirror includes a layer of tungsten formed on the inner surface of thehole.
 5. The electronic system of claim 4, wherein the metallic mirrorincludes a layer of aluminum on the layer of tungsten.
 6. The electronicsystem of claim 5, wherein the layer of aluminum material has athickness of approximately 300 angstroms.
 7. The electronic system ofclaim 1, wherein the hole has an aspect ratio of less than approximately200.
 8. The electronic system of claim 1, wherein the integrated circuitincludes a memory device.
 9. The electronic system of claim 1, whereinthe optical waveguide has a cross-sectional diameter of at least threetimes the cut-off diameter.
 10. An electronic system, comprising: asemiconductor substrate with a hole that includes a diameter in therange of approximately 0.5 microns to approximately 10 microns; anintegrated circuit formed with the semiconductor substrate; an opticalwaveguide formed in the hole in the semiconductor substrate; and anoptical transmitter and an optical receiver associated with the opticalwaveguide that transmits optical signals between selected integratedcircuits of the electronic system.
 11. The electronic system of claim10, wherein the optical waveguide includes a metallic mirror lining inthe hole.
 12. The electronic system of claim 11, wherein the metallicmirror includes a layer of tungsten formed on the inner surface of thehole.
 13. The electronic system of claim 12, wherein the metallic mirrorincludes a layer of aluminum on the layer of tungsten, and wherein thelayer of aluminum material has a thickness of approximately 300angstroms.
 14. The electronic system of claim 13, wherein the a layer ofaluminum is on a silicide.
 15. The electronic system of claim 10,wherein the hole has an aspect ratio of less than approximately
 200. 16.The elecironic system of claim 10, wherein the optical waveguide has across-sectional diameter of at least three times the cut-off diameter.17. The electronic system of claim 10, wherein the optical waveguidecomprises an anodic etch optical waveguide that is lined with a highlyreflective material.
 18. The electronic system of claim 10, wherein aninterior of the optical waveguide is filled with a material having anindex of refraction greater than about
 1. 19. The electronic system ofclaim 10, wherein an interior of the optical waveguide is void.
 20. Anelectronic system, comprising: a semiconductor substrate with a holethat includes an aspect ratio of at least approximately 100; anintegrated circuit formed with the semiconductor substrate; and anoptical waveguide formed in the hole in the semiconductor substrate,wherein an interior of the optical waveguide is filled with a materialhaving an index of refraction greater than about
 1. 21. The electronicsystem of claim 20, wherein the hole has a diameter in the range ofapproximately 0.5 microns to approximately 10 microns.
 22. Theelectronic system of claim 20, wherein the optical waveguide includes ametallic mirror lining in the hole.
 23. The electronic system of claim22, wherein the metallic mirror includes a layer of tungsten formed onthe inner surface of the hole.
 24. The electronic system of claim 23,wherein the metallic mirror includes a layer of aluminum on the layer oftungsten.
 25. The electronic system of claim 24, wherein the layer ofaluminum material has a thickness of approximately 300 angstroms. 26.The electronic system of claim 25, wherein the optical waveguide has across-sectional diameter of at least three times the cut-off diameter.27. The electronic system of claim 20, wherein the hole has an aspectratio of less than approximately
 200. 28. The electronic system of claim20, wherein the integrated circuit includes a memory device.
 29. Theelectronic system of claim 20, wherein the optical waveguide has across-sectional diameter of at least three times the cut-off diameter.30. The electronic system of claim 20, wherein the optical waveguideincludes a lining to substantially reduce loss of optical signals intothe semiconductor substrate and to substantially reduce photogenerationof carriers in the semiconductor substrate.
 31. The electronic system ofclaim 20, wherein the semiconductor substrate includes: a firstsubstrate including a first surface and a second surface opposite to thefirst surface; a first integrated circuit formed in the first surface ofthe first substrate; a second substrate including a first surface and asecond surface opposite to the first surface, wherein the first surfaceof the second substrate is bonded to the second surface of the firstsubstrate; a second integrated circuit formed in the second surface ofthe second substrate; and wherein the optical waveguide is to transmitand receive optical signals between the first and second integratedcircuits.
 32. An electronic system, comprising: a semiconductorsubstrate with a hole that includes an aspect ratio of at leastapproximately 100; an integrated circuit formed with the semiconductorsubstrate; an optical waveguide formed in the hole in the semiconductorsubstrate; and a gallium arsenide transmitter and an optical receiverassociated with the optical waveguide that transmits optical signalsbetween selected integrated circuits of the electronic system.
 33. Theelectronic system of claim 32, wherein the optical receiver comprises asilicon photodiode detector.
 34. The electronic system of claim 32,wherein the semiconductor substrate comprises: a first semiconductorwafer including a first surface and a second surface opposite to thefirst surface, wherein the gallium arsenide transmitter is at the firstsurface of the first semiconductor wafer; a second semiconductor waferincluding a first surface and a second surface opposite to the firstsurface, wherein the optical receiver is at the first surface of thesecond semiconductor wafer, wherein the first surface of the secondsemiconductor wafer is bonded to the second surface of the firstsemiconductor wafer; and wherein the optical waveguide is formed in thefirst semiconductor wafer to transmit and receive optical signalsbetween the gallium arsenide transmitter and the optical receiver. 35.The electronic system of claim 32, wherein the waveguide comprises ahighly reflective inner surface to contain optical signals.
 36. Theelectronic system of claim 32, wherein the hole has a diameter in therange of approximately 0.5 microns to approximately 10 microns.
 37. Theelectronic system of claim 32, wherein the optical waveguide includes ametallic mirror lining in the hole.
 38. The electronic system of claim37, wherein the metallic mirror includes a layer of tungsten formed onthe inner surface of the hole.
 39. The electronic system of claim 38,wherein the metallic mirror includes a layer of aluminum on the layer oftungsten.
 40. The electronic system of claim 39, wherein the layer ofaluminum material has a thickness of approximately 300 angstroms. 41.The electronic system of claim 40, wherein the optical waveguide has across-sectional diameter of at least three times the cut-off diameter.42. The electronic system of claim 32, wherein the optical waveguideincludes an electrically conductive layer.
 43. The electronic system ofclaim 1, wherein the optical waveguide includes an electricallyconductive layer.
 44. The electronic system of claim 43, wherein theoptical waveguide includes a layer of tungsten.
 45. The electronicsystem of claim 43, wherein the optical waveguide includes a layer ofaluminum.
 46. The electronic system of claim 10, wherein the opticalwaveguide includes an electrically conductive layer.
 47. The electronicsystem of claim 21, wherein the optical waveguide is electricallyconductive.
 48. An electronic system, comprising: a first semiconductorwafer including a first surface and a second surface opposite to thefirst surface; a first integrated circuit formed in the first surface ofthe first semiconductor wafer; a second semiconductor wafer including afirst surface and a second surface opposite to the first surface; asecond integrated circuit formed in the first surface of the secondsemiconductor wafer, wherein the first surface of the secondsemiconductor wafer is bonded to the second surface of the firstsemiconductor wafer; and at least one optical waveguide formed in thefirst semiconductor wafer to guide signals between the first and secondintegrated circuits, wherein the waveguide includes an electricallyconductive layer.
 49. The electronic system of claim 48, wherein thewaveguide includes an electrically conductive cladding.
 50. Theelectronic system of claim 48, wherein the optical waveguide includes alayer of tungsten.
 51. The electronic system of claim 48, wherein theoptical waveguide includes a layer of aluminum.
 52. The electronicsystem of claim 48, wherein the optical waveguide comprises a highaspect ratio hole.
 53. The electronic system of claim 52, wherein thehigh aspect ratio hole comprises a highly reflective inner surface tocontain optical signals within the waveguide.
 54. An electronic system,comprising: a semiconductor wafer; an integrated circuit formed on thesemiconductor wafer; the semiconductor wafer including an opticalwaveguide formed in a high aspect ratio hole that extends through thethickness of the semiconductor wafer, wherein the optical waveguideincludes an electrically conductive layer; and an optical transmitterand an optical receiver associated with the optical waveguide thattransmits optical signals between selected integrated circuits of theelectronic system.
 55. The electronic system of claim 54, wherein thenumber of integrated circuits includes a microprocessor and a memorydevice.
 56. The electronic system of claim 54, wherein the opticalwaveguide is formed by an anodic etch that creates a high aspect ratiohole through the semiconductor wafer that is lined with a highlyreflective material.
 57. The electronic system of claim 54, wherein theoptical waveguide includes a metallic mirror that lines an inner surfaceof the high aspect ratio hole.
 58. The electronic system of claim 57,wherein the metallic mirror includes a layer of tungsten formed on theinner surface of the high aspect ratio hole and a layer of aluminumformed outwardly from the layer of tungsten.
 59. The electronic systemof claim 58, wherein the tungsten layer is formed using a siliconreduction process and a silane reduction process.
 60. The electronicsystem of claim 54, wherein the optical waveguide has a cross-sectionaldiameter of at least three times the cut-off diameter.
 61. Theelectronic system of claim 54, wherein the optical waveguide comprises alayer of aluminum material that lines the high aspect ratio holes. 62.The electronic system of claim 61, wherein the layer of aluminummaterial has a thickness of approximately 300 angstroms.